Descriptions of unit, abbreviation, terminology, etc. used throughout the present disclosure are summarized in Table 1.
Aromatic compounds can be alkylated to form different alkylated aromatic products. One that has particular value is para-xylene (e.g., p-xylene). Para-xylene is a valuable substituted aromatic compound because of its great demand for its oxidation to terephthalic acid, a major component in forming polyester fibers and resins. It can be commercially produced from hydrotreating of naphtha (catalytic reforming), steam cracking of naphtha or gas oil, and toluene disproportionation.
Alkylation of toluene with methanol, which is also known as toluene methylation, has been used in laboratory studies to produce para-xylene. Toluene methylation has been known to occur over acidic catalysts, particularly over zeolite catalysts. In particular, ZSM-5 zeolite, zeolite Beta and silicoaluminophosphate (SAPO) catalysts have been used for this process. Generally, a thermodynamic equilibrium mixture of ortho (o)-, meta (m)- and para (p)-xylenes can be formed from the methylation of toluene, as is illustrated by the reaction.

Thermodynamic equilibrium compositions of ortho-, meta-, and para-xylenes can be around 25, 50, and 25 mole %, respectively, at a reaction temperature of 500° C.; though, such toluene methylation can occur over a wide range of temperatures. Para-xylene can be separated from mixed xylenes by a cycle of adsorption and isomerization. Byproducts such as C9+ and other aromatic products can be produced by secondary alkylation of the xylene product.
Unfortunately, there are a number of technical hurdles for toluene methylation to be commercially successful. These include fast catalyst deactivation (e.g., catalyst activity declines to less than or equal to 50% of its initial level when operating at a conversion of greater than or equal to 50%, in a period of 7 days), low methanol selectivity (e.g., only about 40% methanol selectively involves in methylation reaction), and so on. Most of the catalysts, if not all, for toluene methylation show fast catalyst deactivation. Typically, toluene conversion declines with time on stream due to rapid coke formation on the catalyst. Catalyst deactivation is one of the most difficult technical hurdles to overcome for commercial use of toluene methylation.
Accordingly, a method of preparation of a para shape selective catalyst that has increased catalyst stability when used in aromatic alkylation reactions, such as toluene methylation is desirable.